People have often discussed, somewhat in jest, the possibility of installing sprinklers trackside to spice up races. Now while this isn't a serious option due to the cost, the idea has merit in its principles as alot of the overtaking in wet-dry-wet races comes from the track having decent grip off-line.
To understand how this works lets compare the anatomy of an overtake. The driver in front will normally take the racing line, using the outside of the track as the braking zone, moving over to the apex of the corner on the inside of the track then moving to the outside on the exit.
The first and usual approach an overtaking driver will normally use is to try to get inside in the braking zone so he holds the apex of the corner and can use the outside of the track on the exit to maximise speed out of the corner. The big problem with this is that the inside is usually "dirty" e.g. less grip, so the overtaking driver either has brake first, or has too much speed and misses the apex. Either way the advantage is with the driver in front to get to the apex first and get the best exit speed.
The other approach is to sell the driver in front a dummy by lining up on the inside so the driver in front moves inside to block this, then switching back to the outside to take the optimum line. The problem with this approach is that the driver in front still gets to the apex first and hence controls exit speed. If done properly by the driver behind, they will turn in late and cut inside the driver in front on exit, but this doesn't work if the corner is actually a chicane, or the driver in front places the car well and doesn't use the whole width of the track, blocking the driver behind from getting alongside.
In a wet race, there are often two effects on the track. The first is the rain washes out the rubber on the racing line reducing its grip, while simultaneously cleaning up the track offline increasing its grip. This means that drivers find grip where previously there wasn't any and have more variety in how to approach an overtake.
Well what would happen if circuits simulated this by having different types of tarmac across the track? For instance making the braking zone on the inside of corners out of high grip tarmac, and the outside out of low grip? It would mean the racubg line would possibly end up on the inside, but it would also be the worst line for defending the corner on the exit. Laying down another strip of high grip track on the inside of the exit would allow drivers cutting in to get a good exit too. Alternatively if a driver decides to use the traditional racing line, a driver trying an overtake can brake later.
It wouldn't be as artificial as watering the track at random, and more importantly would also still provide a level playing field for all drivers.